Loading system



R. V. L. HARTLEY Dec, 16,

LOADVING SYSTEM filed April 8, 1922 $83 33ml 3533 58:2, .854 k0 tauwmwu nu w T m 5 T W V n k/ w 5 Patented litec. 16, 1924.

UNITED STATES PATENT @FFlfiE.

RALPH V. L. HARTLEY, OF EAST ORANGE, NEW JERSEY, ASSIGNUR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. :21, A CORPORATION OF NEW YORK.

I LOADING SYSTEM.

Application filed April 8,

To all 107mm it may GOHC'GML.

Be it known that I, RALPH V. L. HART- my, a citizen of the United States, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Loading Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to loading systems and more particularly it relates to a. loading system for multiplex signaling circuits.

The loading of a transmission line according to the Pupin system of loading to improve the characteristics of the line for one range of frequencies may sometimes fail to give a corresponding improvement in another range of frequencies or may even prevent the transmission in that range. For example, the loading of a'line or cable for telephone purposes at speech frequencies does not in general give the same uniform transmission and impedance characteristic for the frequencies employed in low frequency telegraph systems. If it were to be loaded to improve its characteristic for telegraph frequencies it probably would have an objectionable attenuation at voice frequencies. An object of this invention is to provide means for loading a line which will be equally effective for a plurality of bands or ranges of frequency in improving the transmission and impedance characteristic of the line, such as, for example, could be employed in a line containing telegraph, telephone and carrier or ultra-audio currents.

This invention, in one form, comprises means for introducing independent systems of loading in the line each of which functions for a particular range of frequencies. At each loading point, currents whose frequencies lie in the various ranges are separated by suitable means such as filters into individual circuits in which are inserted the loading elements appropriate to the particular frequencies present in each channel.

Referring to the drawings, Fig. l represents an embodiment of this invention, in which three different systems of loading are employed.

Fig. 2 is a modification of Fig. l in which 1922. Serial. No. 550,650.

loading elements for each frequency range are not present at each loading station.

Fig. 3 shows how the wave filters in the various channels may be connected in series instead of inparallel as in Figs. 1 and 2.

Fig. t illustrates a loading station in which the loading coil for the low fre quency or telegraph signals is employed at the same time as filtering means for preventing speech frequencies and ultra-audio frequencies from being passed therethrough.

Figs. 5 and 4' represent respectively a high pass filter, and a low pass filter which may be employed in accordance with this invention to separate the frequency ranges to be individually loaded. Figs. (3 and 8 represent band filters which may be employed in accordance with this invention. The letters BF, HP, and LP occurring in the drawing are intended to refer respectively to band filters, high pass lilters, and low pass filters.

Referring to Fig. 1, 10 is'a transmission line provided at distributed points along its length with independent loading means for a plurality of ranges of signaling frequencies. Loading station 11 comprises three parallel channels 12, 13 and 1a in which are present loading coils of the Pupin type l5, l6 and 17. Loading coil 15, for example, may be designed so as to properly load transmission line 10 for the frequencies of importance in speech which, for the purposes of this invention, may be considered to comprise frequencies between 200 cycles and 3000 cycles. Loading coil 16 may be provided for properly loading transmission line 10 for carrier signaling currents which may, for example, be of the order of ten or twenty thousand cycles or more. Loading coil 17 may be properly designed to load transmission line 10 for telegraph currents which, for the purposes of this invention, may be considered to comprise frequencies from zero to 200 cycles.

Since a loading coil designed to give the transmission line 10 the proper impedance characteristic for good quality transmission of signals of one range of frequencies, will,

in general, not function as satisfactorily to improve the impedance characteristic of the line for frequencies outside that range, it will, in general, be found preferable topro vide filters in channels 12, 13 and 1 1 for freely passing those currents to be loaded by each channel but substantially suppressing those currents to be transmitted by the other channels. For example, a band filter should be inserted on each side of loading coil 15 so as to allow currents from 200 cycles per second to 8000 cycles per second to be freely passed therethrough while suppressing currents of frequencies outside that range. Channel 13 may be provided on each side of loading coil 16 with a high pass filter for passing only the carrier current frequencies. Similarly, channel 1 1 may be provided with low pass filters so that channel 14- passes only low frequency telegraph current of 200 cycles per second or less, for example. These filters may be of any desired type and may be, for example, of the type described in detail in the U. S. patent to Campbell No. 1,227,113 of May 22, 1917. Figs. 5, 8 and 7 show respectively a high pass filter, a band filter and a low pass filter of the type disclosed in the above mentioned Campbell patent and the'values the various elements of these filters should have to produce the desired filter action may be readily obtained by reference to the Campbell patent disclosure.

It is preferable, of course, that in the arrangement of Fig. 1, each filter should be terminated in such a way as to offer the highest possible impedance to currents of the frequencies to be suppressed so that the shunting action introduced by each filter does not seriously impair the value of transmission of the frequencies passed by the other channels.

For example, the high pass filter of Fig. 5 and the band pass filter of Fig. 8 should each be terminated in a mid-series section and the low pass filter of Fig. 7 should be terminated by a series arm of a loading section.

Loading stations 20 and 21 are similar to loading station 11, each station comprising independent loading means for telegraph currents, speech currents and carrier currents. Similar loading stations should be distributed throughout the length of the transmission line 10 in a manner already used in standard engineering practice for the loading of transmission lines for speech frequencies only.

In determining the values and the positions for the loading coils for each range of frequencies transmitted by the line it will, in general, be found unnecessary to have at each loading station, a loading coil for each range of frequencies. For example, the loading coils for carrier may be present at every loading station; while the loading coils for speech may be present at every sixth station; and those for telegraph at every tenth station. That is, the system may be readily designed so that the maximum transmission efiiciency for carrier,

speech and telegraph may be arbitrarily chosen for such freqencies that the loading distances for speech and telegraph are even multiples of proper loading distances for carrier. In case it is inconvenient to choose loading distances in this manner it will, therefore, follow that in the ordinary case the loading coils for speech, carrier and telegraph could not be placed at the same points in the line but, in general, would occur at different points thereof.

Fig. 2, for example, shows a plurality, of loading stations for a transmission line 23, loading station 2 1 having a loading coil for all three channels, loading station 25 having a loading coil for only the carrier channel; station 26 having loading coils for only the speech and carrier; and station 27 having loading coils for only telegraph and carrier. It is obvious that such loading stations may be distributed throughout the line to have the proper loading distances for the carrier currents, speech currents and telegraph Lcu'rrents.

In Figs. 1 and 2, the wave filters have been shown connected in parallel with respect to the transmission line. Ifdesired, the filters may be connected in series as shown in Fig. 3. Fig. 6 shows a band filter of the type disclosed in the aforementioned Campbell patent and particularly adapted to use in such a circuit. In this case good qualit transmission will result if each of the filters should terminate in a mid-shunt section.

Due to the fact that the loading coils for telegraph currents will be of fairly high inductance it may sometimes be satisfactory to employ only the loading coil in the telegraph channel at the loading station as shown in Fig. 4, the inductance of the telegraph loading coil being sufiiciently high to prevent the passage of the speech and carrielr frequencies through the telegraph channe Another simplification which may be employed in the telegraph channel at a loading station may be to design the low pass wave filter therein asshown in Fig. 7, such that the shunt capacity of each section of the filter is equal to the total line capacity between the two loading stations. With such an arrangement, the series inductance units of each section of the wave filter will have the proper inductance value for loading the transmission line for telegraph currents and this arrangement, therefore, renders unnecessary having a telegraph loading coil in addition to the low pass filter.

Still other modifications of this invention will be apparent to those skilled in the art without departing from the spirit of the invention as defined in the appended claims. For example, the filter means above described may be simplified a considerable 6X- tent as to number and character of sections in some cases while still obtaining the degree of selectivity desired.

That is claimed is:

1. A signaling line comprising inductive means for periodically loading said line according to the Pupin system for speech frequencies, and independent inductive means for periodically loading said line for frequencies outside the range of frequencies of importance in speech.

2. A signaling line comprising means for periodically loading said line according to the Pupin system for frequencies of importance in speech, and independent means for periodically loading said line for frequencies less than 200 cycles per second.

3. A signaling line comprising inductive means for periodically loading said line according to the Pupin system for speech frequencies, and independent inductive means for periodically loading said line for frequencies greater than the frequencies of importance in speech.

4. A signaling line comprising means for loading said line for speech frequency currents, independent means for loading said line for telegraph signaling currents, and independent means for loading said line for ultra-audio signaling currents.

5. A signaling line comprising means for periodically loading said line accordingto the Pupin system for speech frequencies, independent means for periodically loading said line for frequencies greater than the frequencies of importance in speech, and means for preventing speech frequency currents from passing through the loading means for the second-mentioned frequency range.

6. A signaling line comprising means for periodically loading said line according to the Pupin system for speech frequencies, independent means for periodically loading said line according to the Pupin system for frequencies less than 200 cycles per second, and means for preventing currents of the last mentioned frequency range from passing through said first loading means.

7. A line periodically loaded according to the Pupin system comprising a plurality of individual channels at a loading point, a loading coil in each channel for a particular range of frequencies, and means for selectively transmitting the frequencies to be passedthrough each channel.

8. A signaling line periodically loaded according to the Pupin system comprising a plurality of individual channels at each loading point, a loading coil for a particular range of frequencies in each of a plurality of channels at a plurality of loading points,

and means for passing each range of frequencies only through that channel containing the proper loading unit.

9. A line periodically loaded according to the Pupin system comprising a plurality of ously supplied with a plurality of signal A frequency bands, comprising a plurality of localized loading stations each station comprising a plurality of channels individual to a plurality of said bands, and a loading coil in each of said channels, each of said loading coils having inductance dependent upon the constants of said line and the frequencies individual to the respective channel and determined according to the Pupin system of loading.

11. A loading system comprising at one loading station a plurality of channels individual to a plurality of signaling frequency bands, a loading coil in each of said channels, and a second loading station at a point remote from said first station and comprising a plurality of individual channels for the same frequency bands as for said first station, loading coils in each of said channels less one, said channel in which no loading coil is present being provided with filtering means for freely passing the frequency band desired While suppressing the frequency bands to be passed by the other channels.

12. A signaling line extending between two signal stations and comprising means for periodically increasing the inductance of said line according to the Pup-in system of loading to improve the transmission characteristic of said line for speech frequencies and independent means for periodically in creasing the inductance of said line according to the Pupin system of loading to lin prove the transmission characteristic of said line for frequencies outside the range of frequencies of importance in speech.

13. A signaling line extending between two signaling stations and comprising means for loading said line to improve its transmission characteristic throughout its entire length for speech frequency transmission, independent means for loading said line to improve its transmission characteristic throughout its entire length for low frequency telegraph signals, and independent means for loading said line for improving its transmission characteristic. throughout its entire length for ultra-audio frequency signals.

ltlt.

14. A signaling line comprising means for periodically loading said line according to the Pupin system for soeech frequencies, filtering means inserted in said line at a plurality of points and each comprising an inductance in series with the line and a capacity in shunt to the line, said capacity having a value approximately the same as the dis tributed line capacity between adjacent filtering means, said inductance having such a value with respect to said capacity that said filtering means tends to suppress speech frequencies While improving the transmis sion characteristic for telegraph frequencies.

15. A signaling line comprising means for periodically loading said line according to the Pupin system for telegraph fresaid line at a plurality of points, a capacity associated with each inductance and connected in shunt to the line, each of said capacities having a value approximately equal to the distributed line capacity between adjacent loading points, each of said inductances having such a value with respect to the associated capacity that the combination of inductance and capacity operates as a Wave filter to'suppress the transmission of speech frequencies therethrough.

In Witness whereof, I hereunto subscribe my name this 3rd day of April, A. 11 1922.

RALPH V. L. HARTLEY. 

